Mark brings us good news: the latest version of sigcheck (v2.42) can scan a machine without Internet access in 2 steps. First you scan the machine and save the results in a CSV file, and then you use sigcheck to query VirusTotal from another machine with Internet access.

Let me illustrate with a couple of screenshots.

First of all, just a simple check without VirusTotal:

Then we use option -h to calculate hashes:

And then we add option -c to create a CSV file:

Then we copy the CSV file to another machine with Internet access, and use option -o -v to query VirusTotal using the hashes stored in the CSV file:

This example is for one file. But of course, sigcheck can check many files if you point it to a folder and use option -s to recurse.